Truck load spectra based on weigh-in-motion (WIM) measurements have been utilized in developing live-load models for short and medium-span bridges. The current AASHTO load-and-resistance factor design bridge design (LRFD) specifications were initially calibrated for spans up to 200 ft at the strength limit states. Consequently, the necessity to extend and validate the application of the AASHTO LRFD and load-and-resistance factor rating provisions for long-span bridges becomes evident. This paper presents a framework to establish live-load models for long-span bridges based on WIM data. Multiple years of data from twelve WIM sites are utilized to develop the load spectra. A total of seven types of load effects are considered to satisfy load demands. Parameters that influence the live loads for long-span bridges are identified. The current HL-93 nominal load in AASHTO LRFD results in non-uniform mean maximum load across different loaded lengths; therefore, a length factor for the HL-93 design lane load is proposed to achieve uniform live-load factors. Traffic state (i.e., free-flow or congestion) is found to have a significant impact on the live load for long-span bridges. As the results show that the current AASHTO LRFD load only represents free-flow traffic, a congestion factor is proposed. Additionally, permit vehicles are found to have a significant impact on the live loads under free-flow traffic, but their effect is limited for congested traffic. Statistical live-load models are summarized for reliability calibration.
Lou et al. (Tue,) studied this question.
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